My Ninety-four Year Old Mother Has Been On 25mg Twice

My ninety-four year old mother has been on 25mg twice daily for quite a while. But her diastolic BP got low (55-60) so they, at first, took her off of it entirely and then put her back on half the dosage. But since that happened, she's had three incidents where her pulse "raced". One of those incidents scared her enough she went to the ER. So, my question is: what drug should we discuss with her PCP that would control the heart but not lower her BP?